Compacting machines or compactors are commonly used to compact materials (such as soil, gravel, asphalt, landfill trash) to a desired state of compaction at work sites such as mines and landfills as well as construction sites, such as, for buildings, highways, roads, parking lots and other structures. A wide variety of different compacting systems can be used including self-propelled two-wheel and four-wheel compactors, tow-behind systems, and others. Such compacting machines often are passed over the work materials multiple times in order to achieve the desired compaction. Additionally, work sites, such as roads or foundational structures, may have layers of different materials. For example, a road may have pavement overlying a base material that may, in turn, overlie a sub-base material and a sub-grade material. During construction of a road, compaction machines may compact each individual layer to a desired compaction state before starting construction of the next layer.
The capacity of substrate materials to remain stable over time, support loads or serve as a barrier to liquids, as well as other properties, can depend in significant part upon compacting a given material to a certain compaction state. A variety of different methods can be used to determine the compaction state of work materials. For example, simply passing a compactor over a work site will tend to increase the relative compaction state, and thus the stiffness, of the resident material. Thus, to some extent compactor coverage is a metric which has been used to enable an operator or site manager to estimate that a target state of compaction has been achieved.
Other methods involve using the machine to measure compaction in real-time during the compaction process. For example, compaction may be approximated by determining the ability of the work material to support a compaction machine. Current commercial products quantify ground compaction with an index based on machine performance parameters such as motion resistance, or dynamic response in the case of vibratory compactors. However, compaction is quantified as an index value without engineering units. In particular, the systems that measure compaction during the compaction process typically determine a relative state of compaction of the work material. In other words, the systems determine the extent to which the work material has been compacted relative to the maximum compaction capacity or capability of the compaction machine. As a result, the systems may determine that a work material has been compacted to some percentage of the maximum compacting capability of the machine. Such systems do not provide an absolute or empirical measure of the state of compaction, rather the state of compaction is quantified as a unitless measure.
While knowing a relative state of compaction of a work site can be useful information, many compaction projects require a more sophisticated understanding of the actual compaction state of a material. For example, construction design specification criteria are transitioning from empirical and historical quality requirements to more structural quality requirements. Compaction criteria have traditionally been based on soil compaction measures such as density within an acceptable range of soil moisture, but are more recently moving toward more strength based structural criteria such as soil stiffness and/or modulus. Because compaction machines cannot provide such information in real-time, operators may need to perform secondary tests or evaluations at the work site to validate whether the compaction of the material is meeting the design criteria. Some of the secondary tests may require the removal of material from an otherwise finished work surface. In addition, it may be necessary to perform tests at multiple locations to determine whether the desired level of compaction has been uniformly achieved. Another disadvantage of current real-time compaction measurement methods is that a unitless measure of compaction cannot be used for job site modeling purposes, such as to determine the specific compaction of the soil or other material in order to help design roads, building pads or other foundational structures.
U.S. Patent Application Pub. No. 2013/238305 discloses a method for producing a graphical three-dimensional model of a surface of, for example, a paved road or graded soil. This model may then be compared to a reference-surface model. However, the disclosed method does not involve a determination of a state of compaction of the surface.